Ideally the process is blind to avoid bias but that isn't how most people operate. In this case rejection is based upon his perceived behavior, because abbreviating a last name to a single letter to avoid identification is a lot more common than single letter last names.

This was an article about a dude adding Mr. in front of his name Kim in the CV to land a job.

This is insane but there is a lesson that even a small thing might affect your resume.

Not at all surprising. I used to work with someone whose first name could have been either male or female, so he always included his masculine middle name when signing email, etc.

I assure you they filter based on that and on your top level domain in your email address.